Positive photoresist composition and process for forming resist pattern using same

ABSTRACT

Disclosed are a positive photoresist composition including (A) an alkali-soluble resin, (B) a photosensitizer containing a quinonediazide ester of, e.g., bis[2,5-dimethyl-3-(2-hydroxy-5-methylbenzyl)-4-hydroxyphenyl]methane and (C) e.g., 2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol; and a process including the steps of coating the composition onto a 8 to 12-inch substrate, drying, exposing and developing the same. The composition which can form a pattern having a good shape whose dimensional changes are minimized in a wide range over surface of the substrate, particularly in processes using a large-diameter substrate, and the process for forming a resist pattern using the composition are provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a positive photoresistcomposition having satisfactory sensitivity and definition. Inparticular, it relates to a positive photoresist composition which cangive, in a process for forming a resist pattern using a large-diametersubstrate, satisfactory pattern shapes in which dimensional changes overa wide range of the surface of the substrate are minimized, and toprocess for forming resist pattern using the composition.

[0003] 2. Description of the Related Art

[0004] Positive photoresist compositions comprising an alkali-solubleresin and a quinonediazide ester have been satisfactorily applied inpractical to the production of semiconductor devices and liquid-crystaldisplay devices, since they have excellent definition, sensitivity andetching resistance.

[0005] In the current manufacture of ultralarge-scale integrated circuit(Ultra LSI), a high definition of not more than half a micron, forexample, of 0.4 μm or 0.3 μm is required. There are, therefore, demandson photoresist compositions which can form a resist pattern satisfactoryin definition, exposure margin, focal depth range properties and havinga good shape.

[0006] In development, a puddle development technique is generallyapplied, in which a developer is applied all over the surface of asubstrate from a developer-supplying nozzle disposed above the vicinityof the substrate's center, allowing the substrate to stand for severalseconds and rotating it to remove the developer on the substrate'ssurface through centrifugal force generated by the rotation ofsubstrate. The developer, therefore, is in contact with the substratefor somewhat longer in its center than in its periphery.

[0007] The use of a large-diameter, 8-to 12-inch substrate has beenconsidered instead of a conventional 6-inch substrate, in order toenhance the throughput and productivity of semiconductor chips. In sucha large-diameter substrate, however, the puddle developing techniqueinvites tapering of a pattern and reduction in thickness of a resultantfilm in the center of substrate, which results in deteriorated yield ofproduction.

[0008] In particular, when a resist pattern of not more than half amicron is formed, twist of pattern formation occurs in the substrate'scenter and the yield is reduced, and hence the enhancement of thethroughput can hardly be achieved.

[0009] On the other hand, a variety of high-definition positivephotoresist compositions have been reported which are directed toquinonediazide esters as photosensitizers (e.g., Japanese PatentLaid-Open Nos. 8-245461, 6-167805, 7-152152, 7-159990, 7-168355,7-175213, 7-219220, 7-261382, 7-129255, 8-146602, 8-254824, 8-339079,9-15854, 9-96904, 9-110755, 9-110757, 9-110760, 9-110762, 9-127690,9-179293, 9-258437, 9-281702, 9-286751, 9-286752, 9-286753, 9-291054,9-291055 and 9-291056).

[0010] These compositions exhibit high definition but are stillinsufficient to reduce dimensional changes in resist patterns on thesurface of a substrate, and are still insufficient for the applicationto a large-diameter substrate in order to enhance the throughput.

[0011] Demands have, therefore, been made to provide positivephotoresist compositions which can form a resist pattern of not morethan half a micron having a good shape whose inplane dimensional changesare minimized over a substrate's surface.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the present invention to providea positive photoresist composition which can form a resist pattern ofnot more than half a micron having a good shape in which dimensionalchanges over a wide range of the surface of a substrate are minimized,and to provide, particularly in a resist pattern forming process using alarge-diameter substrate, a process for forming a resist pattern usingthe composition.

[0013] After the intensive investigations, the present inventors havesolved the above problems of conventional techniques.

[0014] To be more specific, the present invention provides a positivephotoresist composition comprising (A) an alkali-soluble resin, (B) aphotosensitizer containing a quinonediazide ester of a compound of thefollowing formula (I):

[0015] wherein each of R¹ and R² is independently a methyl group or anethyl group, and (C) at least one of phenol group-containing compoundsgiving an elution time ranging from 6 to 30 minutes in high performanceliquid chromatography determined under the following conditions:

[0016] eluent: a mixed solvent ofwater/tetrahydrofuran/methanol=40/24/36 (by weight); column: 4.6 mm(diameter)×150 mm (length) containing 5 μm silica gel as a filler(carbon content being about 15%); column temperature: 45.0° C.; supplyrate of eluent: 0.700 ml/min.

[0017] The compound represented by the formula (I) in the compositionmay be a compound of the following formula:

[0018] In addition, the compound represented by the formula (I) in thecomposition may be a compound of the following formula (Ib):

[0019] In the above composition, the content of Ingredient (C) maypreferably range from 5% to 50% by weight relative to Ingredient (A).

[0020] The phenol-group containing compound, Ingredient (C), of theaforementioned composition may be at least one compound selected from:

[0021] The invention provides, in another aspect, a process for forminga resist pattern comprising the steps of:

[0022] (1) coating the aforementioned positive photoresist compositiononto a substrate having a diameter of 8 to 12 inches, and drying thecoated substrate to form a resist film,

[0023] (2) subjecting the resist film to selective exposure through amask,

[0024] (3) heating the exposed resist film, and

[0025] (4) removing the resist film at exposed positions by an aqueousalkali solution.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] These and other features, objects, and advantages of the presentinvention will become apparent upon a consideration of the followingdescription of the invention when read in conjunction with the drawings,in which:

[0027]FIG. 1 illustrates a developing process and locations for theevaluation of sensitivity on resist patters in the examples of theinvention;

[0028]FIG. 2 is a chromatogram of the compound c1 used in the examples;

[0029]FIG. 3 is a chromatogram of the compound d1 used in the examples;

[0030]FIG. 4 is a chromatogram of an elution pattern of benzene; and

[0031]FIG. 5 is a chromatogram of an elution pattern of toluene.

DETAILED DESCRIPTION OF THE INVENTION

[0032] (A) Alkali-soluble resin

[0033] An alkali-soluble resin used as Ingredient (A) is not limited andcan be liberally chosen from those generally used as film-formingsubstances in positive photoresist compositions.

[0034] Examples of the alkali-soluble resins include condensates ofaromatic hydroxyl compounds and aldehydes or ketones,polyhydroxystyrenes and their derivatives.

[0035] The aromatic hydroxyl compounds include, for example, phenol,m-cresol, p-cresol, o-cresol, 2,3-xylenol, 2,5-xylenol, 3,5-xylenol,3,4-xylenol and other xylenols; m-ethylphenol, p-ethylphenol,o-ethylphenol, 2,3,5-trimethylphenol, 2,3,5-triethylphenol,4-tert-butylphenol, 3-tert-butylphenol, 2-tert-butylphenol,2-tert-butyl-4-methylphenol, 2-tert-butyl-5-methylphenol and otheralkyl-substituted phenols; p-methoxyphenol, m-methoxyphenol,p-ethoxyphenol, m-ethoxyphenol, p-propoxyphenol, m-propoxyphenol andother alkoxy-substituted phenols; o-isopropenylphenol,p-isopropenylphenol, 2-methyl-4-isopropenylphenol,2-ethyl-4-isopropenylphenol and other isopropenyl-substituted phenols;phenylphenol and other aryl-substituted phenols; 4,4′-dihydroxybiphenyl,bisphenol A, resorcinol, hydroquinone, pyrogallol and otherpolyhydroxyphenols. These aromatic hydroxyl compounds can be used singlyor in combination.

[0036] As suitable examples of the aldehydes, there may be mentionedformaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde,butylaldehyde, trimethylacetaldehyde, acrolein (acrylaldehyde),crotonaldehyde, cyclohexanaldehyde, furfural, furylacrolein,benzaldehyde, terephthalaldehyde, phenylacetaldehyde,α-phenylpropylaldehyde, β-phenylpropylaldehyde, o-hydroxybenzaldehyde,m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, o-methylbenzaldehyde,m-methylbenzaldehyde, p-methylbenzaldehyde, o-chlorobenzaldehyde,m-chlorobenzaldehyde, p-chlorobenzaldehyde, and cinnamaldehyde. Each ofthese aldehydes may be used independently or in combination.

[0037] Practical examples of the ketones include acetone, methyl ethylketone, diethyl ketone and diphenyl ketone. Each of these ketones may beused singly or in combination. Further, an optional combination of anyof aldehydes and any of ketones can be employed.

[0038] The condensate of an aromatic hydroxyl compound and an aldehydeor a ketone can be prepared in the presence of an acidic catalystaccording to a known technique. Such an acidic catalyst includes, forinstance, hydrochloric acid, sulfuric acid, formic acid, oxalic acid andp-toluenesulfonic acid.

[0039] As the polyhydroxystyrenes and their derivatives, there may bementioned, for example, vinylphenol homopolymers, copolymers ofvinylphenol and a copolymerizable comonomer. Such a comonomer includesacrylic acid derivatives, acrylonitrile, methacrylic acid derivatives,methacrylonitrile, styrene, α-methylstyrene, p-methylstyrene,o-methylstyrene, p-methoxystyrene, p-chlorostyrene and other styrenederivatives.

[0040] Of these alkali-soluble resins used in the present invention asIngredient (A), novolak resins obtained from a phenol compound such asm-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, 2,3,5-trimethylphenol, andan aldehyde such as formaldehyde are advantageously used since they areeffective in achieving high thermostability. Incidentally, low molecularweight fractions of the novolak resin have been removed. In particular,preferred are novolak resins containing 5% to 40% by mole of p-cresol,and, in addition, m-cresol and 2,5-xylenol as constitutive units andhaving an ortho-ortho bonding content of 20% to 80%.

[0041] The weight average molecular weight of the novolak resin shouldrange from 2,000 to 25,000, preferably from 2,500 to 20,000 and morepreferably from 5,000 to 10,000, while the resin should comprise no lowmolecular weight fraction. The term “weight average molecular weight” asused herein is defined as the value in terms of polystyrene measured bygel permeation chromatography (GPC).

[0042] The removal of low molecular weight fractions can be conducted byfractionation or other treatments. The fractionation is carried out by,for example, a process of dissolving a resin obtained by condensation ina good solvent and adding the resultant solution into water to therebyform precipitates. The good solvent includes, for instance, methanol,ethanol and other alcohols, acetone, methyl ethyl ketone and otherketones, ethylene glycol monoethyl ether acetate, and tetrahydrofuran.

[0043] (B) Photosensitizer

[0044] The photosensitizer (B) used in the composition of the inventionis a photosensitizer containing a quinonediazide ester, and preferablycontaining a quinonediazide ester of the compound represented by theformula (I).

[0045] In particular, quinonediazide esters of the compounds representedby the formulae (Ia) and (Ib) are practically preferred among those ofthe compounds of the formula (I).

[0046] The average esterification ratio of the compound represented bythe formula (I) is preferably 50%, in other words, the ester maypreferably be diester-rich. The term “diester-rich” used herein meansthe peak area ratio of a diester determined at 254 nm by highperformance liquid chromatography is relatively larger than any peakarea ratios of other mono-, tri- and tetra-esters. Mono-, tri-,tetra-esters may be formed to some extent by the esterification, andthese esters can be present in Ingredient (B).

[0047] The content of the quinonediazide ester of the compoundrepresented by the formula (I) in Ingredient (B) may preferably be equalto or more than 50% by weight and more preferably equal to or more than70% by weight. When the content is less than 50% by weight, definitionis deteriorated and dimensional changes in resist pattern over thesubstrate's surface cannot sufficiently be minimized.

[0048] Any other quinonediazide esters than the above esters can be usedconcurrently, but the amount of such other ester may preferably be lessthan 50% by weight in Ingredient (B).

[0049] The other quinonediazide esters are esters between hydroxylcompounds other than above and quinonediazide compounds. The hydroxylcompounds includebis[3-(3,5-dimethyl-4-hydroxybenzyl)-4-hydroxy-5-methylphenyl]methane,bis[3-(3,5-dimethyl-4-hydroxybenzyl)-4-hydroxy-5-ethylphenyl]methane,bis[3-(3,5-diethyl-4-hydroxybenzyl)-4-hydroxy-5-methylphenyl]methane,bis[3-(3,5-diethyl-4-hydroxybenzyl)-4-hydroxy-5-ethylphenyl]methane andother terminal xylenol linear tetranuclear compounds;2,4-bis[2-hydroxy-3-(4-hydroxybenzyl)-5-methylbenzyl]-6-cyclohexylphenol,2,4-bis[4-hydroxy-3-(4-hydroxybenzyl)-5-methylbenzyl]-6-cyclohexylphenoland other linear pentanuclear compounds and other linear polyphenoliccompounds;bis[2-hydroxy-3-(3,5-dimethyl-4-hydroxybenzyl)-5-methylphenyl]methane,bis[2-hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylphenyl]methane,bis[4-hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylphenyl]methane,bis[2,5-dimethyl-3-(4-hydroxy-5-methylbenzyl)-4-hydroxypheny methane,bis[2,5-dimethyl-3-(4-hydroxybenzyl)-4-hydroxyphenyl]methane,bis[2,5-dimethyl-3-(2-hydroxybenzyl)-4-hydroxyphenyl]methane and otherlinear tetranuclear compounds; 2,3,4-trihydroxybenzophenone,2,4,4′-trihydroxybenzophenone, 2,4 ,6-trihydroxybenzophenone,2,3,4,4′-tetrahydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone,2,3′,4,4′,6-pentahydroxybenzophenone,2,2′,3,4,4′-pentahydroxybenzophenone,2,2′,3,4,5′-pentahydroxybenzophenone,2,3′,4,5,5′-pentahydroxybenzophenone,2,3,3′,4,4′,5′-hexahydroxybenzophenone and otherpolyhydroxybenzophenones;bis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane,1,4-bis[1-(3,5-dimethyl-4-hydroxyphenyl)isopropyl]benzene, 2,4-bis(3,5-dimethyl-4-hydroxyphenylmethyl)-6-methylphenol,bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene,1-[1-(3-methyl-4-hydroxyphenyl)isopropyl]-4-[1,1-bis(3-methyl-4-hydroxyphenyl)ethyl]benzene,2,6-bis[1-(2,4-dihydroxyphenyl)isopropyl]-4-methylphenol, 4,6-bis[1-(4-hydroxyphenyl)isopropyl]resorcin,4,6-bis(3,5-dimethoxy-4-hydroxyphenylmethyl)pyrogallol,4,6-bis(3,5-dimethyl-4-hydroxyphenylmethyl)pyrogallol,2,6-bis(3-methyl-4,6-dihydroxyphenylmethyl)-4-methylphenol,2,6-bis(2,3,4-trihydroxyphenylmethyl)-4-methylphenol,1,1-bis(4-hydroxyphenyl)cyclohexane and other hydroxyaryls; phenol,p-methoxyphenol, dimethylphenol, hydroquinone, bisphenol A, naphthol,pyrocatechol, pyrogallol monomethyl ether, pyrogallol-1,3-dimethylether, gallic acid, partially esterified or partially etherified gallicacid and other phenols.

[0050] The photosensitizer (B) in the composition of the presentinvention comprises an ester between any of the hydroxyl compounds asmentioned above and a quinonediazide compound. The quinonediazidecompound includes, for example, naphthoquinone-1,2-diazidesulfonylhalides, o-benzoquinonediazidesulfonyl halides,o-anthraquinonediazidesulfonyl halides. Of these compounds,naphthoquinone-1,2-diazide-5-sulfonyl chloride,naphthoquinone-1,2-diazide-4-sulfonyl chloride,naphthoquinone-1,2-diazide-6-sulfonyl chloride and othernaphthoquinone-1,2-diazidesulfonyl halides are preferred. Theesterification can be conducted according to a conventional technique.

[0051] The amount of Ingredient (B) in the composition of the presentinvention may preferably fall in the range from 10% to 60% by weight andmore preferably from 20% to 50% by weight relative to the total amountof Ingredient (A), alkali-soluble resin, and Ingredient (C). When theamount of Ingredient (B) is less than the above range, images in exactaccordance with a pattern cannot be obtained and transfer property isdeteriorated. When it exceeds the above range, the sensitivity anduniformity of a formed resist film are decreased, and the definition isdeteriorated.

[0052] (C) Phenol group-containing compound

[0053] The term “phenol group-containing compound (C)” used in thecomposition of the present invention means any of phenolgroup-containing compounds which elute from a column within the specificelution time range when high performance liquid chromatography isconducted under the specific eluent, column, column temperature andsupply rate of the eluent. The conditions of high performance liquidchromatography are described below:

[0054] Eluent: a solvent mixture ofwater:tetrahydrofuran:methanol=40:24:36 (by weight)

[0055] Column: silica gel having a particle size of 5 μm is used as afiller (carbon content: about 15%), and the column size is 4.6 mm indiameter and 150 mm in length. The filler is preferably silica gelobtained by chemically bonding octadecyl groups to silicon in silicagel. As the column, Intersil ODS-2 (trade name, manufactured by GLSience) can for example be used. In columns which can be used in thepresent invention, benzene and toluene respectively elute at about 6.231minutes and at about 8.284 minutes, and the performances of columns tobe used can be verified using these compounds. FIGS. 4 and 5respectively illustrate chromatograms indicating elution patters ofbenzene and toluene.

[0056] Column temperature: 45.0° C. The column temperature can beadjusted through a thermoregulated bath or an oven.

[0057] Supply rate of eluent: 0.700 ml/min.

[0058] The elution time may fall in the range from 6 to 30 minutes,preferably from 7 to 15 minutes and particularly preferably from 8 to 12minutes. When the elution time is less than 6 minutes, tapering ofpattern and reduction in thickness in the substrate's center seriouslyoccur and when it exceeds 30 minutes, the sensitivity is remarkablydeteriorated.

[0059] The use of Ingredient (C) can advantageously suppress dimensionalchanges in resist pattern over a substrate. This advantage issignificant particularly in puddle developing technique using alarge-diameter substrate of about 8 to 12 inches.

[0060] As examples of the phenol group-containing compounds, Ingredient(C) which meet the above conditions, there may be mentioned compoundsrepresented by the formulae (c1) through (c6). The elution times of thecompounds of formulae (c1), (c2), (c3), (c4), (c5) and (c6) are,respectively, 10.159 min., 6.57 min., 10.700 min., 9.952 min., 7.445min., and 8.94 min.

[0061] The composition of the invention, where Ingredient (B) andIngredient (C) are used in combination, can provide suppressing effectsfor minimizing dimensional changes in resist pattern over a substrate,in particular suppressing effect of pattern tapering and reduction inthickness in the center of a substrate, even when a large-diametersubstrate is employed.

[0062] The amount of Ingredient (C) can be selected within the rangefrom 5% to 50% by weight and preferably from 10% to 35% by weightrelative to the alkali-soluble resin, Ingredient (A).

[0063] The composition of the present invention can further comprise anyof polyphenol compounds known as sensitizers (sense amplifiers).

[0064] By way of example, the compounds represented by the formula (I)or other compounds can be employed. Typical examples of the polyphenolcompounds includebis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane, 1,4-bis[1-(3,5-dimethyl-4-hydroxyphenyl)isopropyl]benzene, 2,4-bis(3,5-dimethyl-4-hydroxyphenylmethyl)-6-methylphenol,bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane,bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane,1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene,1-[1-(3-methyl-4-hydroxyphenyl)isopropyl]-4-[1,1-bis(3-methyl-4-hydroxyphenyl)ethyl]benzene,2,6-bis[1-(2,4-dihydroxyphenyl)isopropyl]-4-methylphenol,4,6-bis[1-(4-hydroxyphenyl)isopropyl]resorcin,4,6-bis(3,5-dimethoxy-4-hydroxyphenylmethyl)pyrogallol,4,6-bis(3,5-dimethyl-4-hydroxyphenylmethyl)pyrogallol,2,6-bis(3-methyl-4,6-dihydroxyphenylmethyl)-4-methylphenol,2,6-bis(2,3,4-trihydroxyphenylmethyl)-4-methylphenol,1,1-bis(4-hydroxyphenyl)cyclohexane,2,6-bis(3,5-dimethyl-4-hydroxybenzyl)-4-methylphenol,bis(3,5-dimethyl-4-hydroxyphenyl)-2-hydroxyphenylmethane,2,4-bis(3,5-dimethyl-4-hydroxybenzyl)-5-hydroxyphenol, andbis(3,5-dimethyl-4-hydroxyphenyl)-3,4-dihydroxyphenylmethane.

[0065] The content of the sensitizer, if added, may fall in the rangefrom 5% to 50% by weight, and preferably from 10% to 35% by weightrelative to the alkali-soluble resin, Ingredient (A).

[0066] Where necessary, the composition may further comprise any ofcompatible additives including, for example, ultraviolet absorbents forinhibition of halation and surfactants for prevention of striationwithin a range not adversely affecting the objects of the presentinvention. Examples of the ultraviolet absorbents include2,2′,4,4′-tetrahydroxybenzophenone,4-dimethylamino-2′,4′-dihydroxybenzophenone,5-amino-3-methyl-1-phenyl-4-(4-hydroxyphenylazo)pyrazole,4-dimethylamino-4′-hydroxyazobenzene,4-diethylamino-4′-ethoxyazobenzene, 4-diethylaminoazobenzene andcurcumin. As the surfactants, there may be mentioned, for instance,Fluorade FC-430 and FC-431 (trade names, manufactured by Sumitomo 3MLtd., Japan), F-TOP EF122A, EF122B, EF122C and EF126 (trade names,manufactured by Tochem Products Ltd., Japan) and otherfluorine-containing surfactants.

[0067] The composition of the present invention may preferably be usedas a solution obtained by dissolving Ingredients (A), (B) and (C), andeach of ingredients added according to necessity, in a proper solvent.

[0068] Practical examples of the solvent include solvents conventionallyused for positive photoresist compositions, such as acetone, methylethyl ketone, cyclohexanone, methyl isoamyl ketone, 2-heptanone andother ketones; ethylene glycol, propylene glycol, diethylene glycol,ethylene glycol monoacetate, propylene glycol monoacetate, diethyleneglycol monoacetate, or their monomethyl ethers, monoethyl ethers,monopropyl ethers, monobutyl ethers or monophenyl ethers and otherpolyhydric alcohols and their derivatives; dioxane and other cyclicethers; and ethyl lactate, methyl acetate, ethyl acetate, butyl acetate,methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethylethoxypropionate and other esters. Each of these solvents may be usedsolely or in combination. In particular, acetone, methyl ethyl ketone,cyclohexanone, methyl isoamyl ketone, 2-heptanone and other ketones;ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, methylpyruvate, ethyl pyruvate, methyl methoxypropionate, ethylethoxypropionate and other esters are desirable.

[0069] Practically, the composition may be used, for example, in thefollowing manner: Each of Ingredients (A), (B) and (C), and otheringredients added according to necessity is dissolved in a propersolvent as mentioned above to give a coating solution; the coatingsolution is then applied, using a spinner or the like, onto a substratesuch as a silicon wafer or a substrate on which an adhesion promotercoat or an antireflection coating has been formed, and subsequentlydried to form a photosensitive layer; next, the photosensitive layer isirradiated and exposed with an ultraviolet ray source such as alow-pressure mercury lamp, a high-pressure mercury lamp, anultra-high-pressure mercury lamp, or a xenon lamp, through a desiredmask pattern, or irradiated with a scanning electron beam; and theexposed portions of the film are then dissolved and removed by droppinga developer solution, for example, an alkaline aqueous solution such asa 1% to 10% by weight tetramethylammonium hydroxide (TMAH) aqueoussolution from a developer dropping nozzle disposed above the vicinity ofthe center of substrate, thus covering all over the surface of thesubstrate with the developer; allowing the substrate to stand for 50 to60 sec. and then rotating the substrate by a spinner to remove thedeveloper, thus forming an image being in exact accordance with the maskpattern.

EXAMPLES

[0070] The present invention will be further illustrated in detail withreference to several inventive examples and comparative examples below.

[0071] Each of the characteristics of the positive photoresistcompositions was evaluated according to the following manner,respectively.

[0072] (1) Sensitivity:

[0073] A sample was applied onto a 8-inch silicon wafer using a spinner,and dried on a hot plate at 90° C. for 90 sec. to form a resist filmhaving a thickness of 1.05 μm. The resist film was then irradiated foran increasing period from 0.1 sec. at intervals of 0.01 sec. using areducing-type projection aligner NSR-2005il0D (manufactured by NikonCorporation, Japan; NA=0.57). The film was then post-exposure baked(PEB) at 110° C. for 90 sec.; subjected to puddle developing in a 2.38%by weight tetramethylammonium hydroxide (TMAH) aqueous solution at 23°C., washed with water for 30 sec., and dried. In this procedure, thesensitivity was defined as the exposure time period (ms) to give exposedportion having a thickness of zero after development.

[0074] The developing process will be described in detail with referenceto FIG. 1. FIG. 1 illustrates the developing process and locations wherethe sensitivity was evaluated on resist patterns in the examples of theinvention,. The silicon wafer was provided with a total of 81 resistpatterns in 81 blocks including α1, α2, α3 . . . α81 (one block was 20mm×20 mm). The block in the substrate's center was designated as “blockb” and four blocks in the periphery at 80 mm distance from the centerwere designated as “blocks a”. The developing was carried out in thefollowing manner using a tubular nozzle developing device (product name:TR6132UD, Tatsumo K. K., Japan) and the evaluation of sensitivity wascarried out on the block a in FIG. 1.

[0075] Developing process

[0076] Onto a substrate after post exposure baked (PEB), the developerwas dropped from above the block b in FIG. 1 under a discharge pressureof 0.7 kg/cm³, at discharge rate of 0.6 L/min over 7 sec., the substratewas then allowed to stand for 53 sec. (the developing time period was atotal of 60 sec.=7 sec.+53 sec.), and washed with pure water at 3000 rpmfor 30 sec. to remove the developer above the surface of substrate.

[0077] (2) Definition:

[0078] The definition was defined as the critical definition at anexposure which reproduced a 0.35 μm mask pattern.

[0079] The evaluation of the definition was conducted on resist patternson the periphery of substrate (blocks a in FIG. 1).

[0080] (3) Focal Depth Range Properties:

[0081] A sample was subjected to exposure and development using areducing-type projection aligner NSR-2005il0D (manufactured by NikonCorporation, Japan; NA=0.57) at an exposure of Eop (the exposure timeperiod to reproduce the set dimensions of mask pattern (line width 0.35μm, line-and-space (L&S) 1:1) as a standard exposure, where the focuswas shifted up and down at this exposure. The obtained resist patternwas subjected to an SEM photographic observation. Based upon the SEMphotograph, the focal depth range was defined as the maximum value (μm)of the focal shift (defocus) to obtain a 0.35 μm rectangular resistpattern within a variation of ±10% of the set dimensions.

[0082] The focal depth range properties were evaluated on resistpatterns on the periphery of substrate (blocks a in FIG. 1).

[0083] (4) Evaluation of Dimensional Changes:

[0084] When a 0.35 μm resist pattern was obtained on the periphery ofsubstrate (block a in FIG. 1), the size of a resist pattern formed inthe substrate's center (block b in FIG. 1) was defined as x μm, and thedimensional change rate (decreasing rate) was calculated according tothe following equation:

Dimensional change rate (decreasing rate)=[(0.35−x)/0.35]×100 (%)

[0085] (5) Evaluation of Yield:

[0086] A total of 81 resist patterns of the identical shape were formedon a 8-inch silicon wafer in the manner as in Evaluation (1), thesensitivity (FIG. 1).

[0087] On each of the 81 resist patterns, the dimensional changes wereevaluated in the manner as in Evaluation (4), and the total number ofresist patterns whose change rates were less than 10% was defined as y,and the yield was calculated according to the following equation:

Yield=(y/81)×100(%)

EXAMPLE 1

[0088] Ingredient (A):

[0089] Alkali-soluble novolak resin: 100 parts by weight [a resincomposed of m-cresol:p-cresol:2,5-xylenol=5:1:4 (by mole) whose lowmolecular weight fractions were removed (Mw=6800, ortho-ortho bondingcontent 45%)]

[0090] Ingredient (B):

[0091] b1:b2=7:1 (by weight): 57 parts by weight [b1:diester ofbis[2,5-dimethyl-3-(2-hydroxy-5-methylbenzyl)-4-hydroxyphenyl]methane(compound represented by the formula (Ia)), b2: triester of methylgallate]

[0092] Ingredient (C):

[0093] c1: 33 parts by weight [c1:2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol (compoundrepresented by the formula (c1), elution time: 10.159 min.)]

[0094] A positive photoresist composition was obtained by dissolving theabove Ingredients (A), (B) and (C) in 470 parts by weight of2-heptanone, and filtering the solution with a membrane filter having apore size of 0.2 μm.

[0095] The determination using high performance liquid chromatographywas conducted in the following manner:

[0096] (i) A sample was dissolved in tetrahydrofuran to give a 0.5% byweight sample solution.

[0097] (ii) An eluent of water:tetrahydrofuran:methanol=40:24:36 (byweight) was passed through a column at a supply rate of 0.700 ml/min for10 minutes. The column was composed of 5 μm silica gel as a filler(carbon content being about 15%) and had a column size of 4.6 mm indiameter ×150 mm in length (product name: Intersil ODS-2, GL Science).The column temperature was adjusted to 45.0° C. using an oven.

[0098] (iii) The sample solution (1.0 μl) was injected into thechromatograph, and the elution time of the sample detected in thevicinity of 280.4 nm was determined.

[0099] Table 1 demonstrates the elution times of the samples c1 throughc6 and d1 through d4 respectively used in the inventive examples andcomparative examples. TABLE 1 Sample Elution Time (min) c1 10.159 c26.570 c3 10.700 c4 9.952 c5 7.445 c6 8.940 d1 5.338 d2 4.317 d3 5.254 d45.569

[0100] Chromatograms of c1 and d1 are illustrated in FIGS. 2 and 3,respectively.

EXAMPLES 2 TO 10 AND COMPARATIVE EXAMPLES 1 TO 4

[0101] A series of samples were prepared and their characteristics wereevaluated in a similar manner as in Example 1, except that each ofIngredient (B), Ingredient (C), the sensitizer and developing time(standing time) was changed as indicated in Table 2 below.

[0102] Table 3 demonstrates the above characteristics (1) through (5) oncoating compositions prepared in Examples 1 through 10 and ComparativeExamples 1 though 4. TABLE 2 Ingredient Developing Ingredient (C)Sensitizer Time Example (B) (wt %) (wt %) (sec.) 1 b1/b2 c1 — 60 (7/1)(33) 2 b1/b2 c2 — 60 (7/1) (33) 3 b1/b2 c3 — 75 (7/1) (33) 4 b1/b2 c4 —75 (7/1) (33) 5 b1/b2 c5 — 45 (7/1) (33) 6 b1/b2 c6 — 45 (7/1) (33) 7b1/b2 c1/c5 — 60 (7/1) (1/1) (33) 8 b1/b2 c2/c6 — 45 (7/1) (3/7) (33) 9b3/b2 c1/c5 — 60 (7/1) (1/1) (33) 10  b1/b2 c5 d1 45 (7/1) (15) (15)Comp. ex. b4/b2 c1 — 60 1 (7/1) (33) Comp. ex. b1/b2 — d2 60 2 (7/1)(33) Comp. ex. b1/b2 — d3 60 3 (7/1) (33) Comp. ex. b1/b2 — d4 60 4(7/1) (33)

[0103] TABLE 3 Focal depth dimensional Sensitivity Definition rangechange rate Yield Example (ms) (μm) properties (%) (%) 1 460 0.30 1.210.86 88.89 2 460 0.30 1.2 10.57 90.12 3 440 0.28 1.0 15.14 62.96 4 4000.28 1.0 15.71 60.49 5 550 0.26 1.2 15.14 61.73 6 490 0.28 1.0 16.0060.49 7 490 0.28 1.4 14.29 69.14 8 450 0.30 1.2 14.00 65.43 9 520 0.261.2 13.71 74.07 10  520 0.28 1.2 16.57 59.25 Comp. ex. 400 0.30 0.822.86 44.44 1 Comp. ex. 460 0.30 1.0 21.43 50.62 2 Comp. ex. 440 0.300.8 25.71 39.51 3 Comp. ex. 400 0.28 1.2 31.43 34.57 4

[0104] According to the present invention, a positive photoresistcomposition can be obtained, which can form a resist pattern of not morethan half a micron having a good shape in which dimensional changes areminimized over a wide range of a substrate, and give satisfactory focaldepth range properties and yield.

[0105] The process for the formation of resist patterns using thecomposition of the invention is advantageous particularly in processesusing a large-diameter substrate.

[0106] While the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to one ofordinary skill in the art that various changes and modifications can bemade therein without departing from the spirit and scope thereof.

What is claimed is:
 1. A positive photoresist composition comprising (A)an alkali soluble resin, (B) a photosensitizer containing aquinonediazide ester of a compound of the following formula (I):

wherein each of R¹ and R² is independently a methyl group or an ethylgroup, and (C) at least one compound of phenol group-containingcompounds giving an elution time in the range from 6 to 30 minutes inhigh performance liquid chromatography, said high performance liquidchromatography being conducted under the following conditions: eluent: amixed solvent of water:tetrahydrofuran:methanol=40:24:36 (by weight);column: 4.6 mm (diameter)×150 mm (length) containing 5 μm silica gel asa filler (carbon content being about 15%); column temperature: 45.0° C.;supply rate of eluent: 0.700 ml/min.
 2. The composition according toclaim 1, wherein said compound represented by the formula (I) is acompound of the following formula (Ia):


3. The composition according to claim 1, wherein said compoundrepresented by the formula (I) is a compound of the following formula(Ib):


4. The composition according to claim 1, wherein the content ofIngredient (C) ranges from 5% to 50% by weight relative to Ingredient(A).
 5. The composition according to claim 1, wherein said phenolgroup-containing compound, Ingredient (C), is at least one compoundselected from the group consisting of the following compounds (c1)through (c6):


6. A process for forming a resist pattern comprising the steps of: (1)coating the positive photoresist composition of claim 1 onto a substratehaving a diameter ranging from 8 to 12 inches, and drying the coatedsubstrate to form a resist film, (2) subjecting said resist film toselective exposure though a mask, (3) heating said resist film, and (4)removing the resist film at exposed positions by an aqueous alkalisolution.